Add-event form behaviour

- [x] Submit show "thank you"
- [x]  Ability to add similar event
- [ ]  Add feedback on what other events are stored for this venue
- [ ]  Warning if starting time is in morning-hour (between 0:00-6:00) 
- [ ]  Date formField should not show past dates (use native date input?) 
- [x]  Redesign field errors ("Foo is required") (CM done)